The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Flexible fuel vehicles (FFVs) are designed to run on a variety of fuels, for example: gasoline, alcohol/gasoline blends, such as 85% ethanol (E85), or a combination of gasoline and alcohol/gasoline blends that result in a random fuel alcohol percent. An engine operating on an alcohol/gasoline blend requires an increased amount of fuel in an air-to-fuel (A/F) ratio compared to gasoline at stoichiometry. For instance, at stoichiometry, the E85 A/F ratio is near 9:1, while gasoline's A/F ratio is near 14.5:1.
Traditionally, “fuel consumed” and “average fuel economy” data are displayed in many vehicles on a Driver Information Center (DIC). Fuel consumption volume may be determined by dividing the mass of fuel consumed by its density. In the past it has been possible to use a fixed fuel density value to calculate the consumption of fuel due to the narrow range of possible density values available. Traditionally, an average fuel density of approximately 735,000 mg/liter was used regardless of the density of the fuel actually being consumed. However, calculating fuel consumption for FFVs based on an average fuel density of gasoline, may result in inaccurate fuel consumption values because the density of ethanol is 8-10% higher than gasoline.
When a driver refuels an FFV, fuel alcohol percent may change significantly with the addition of new fuel. For example, E85 or gasoline may be introduced into a fuel tank containing gasoline or some alcohol/gasoline blend, potentially resulting in a new fuel alcohol percent. A change in the fuel alcohol percent results in a change in fuel density. Using a fixed fuel density suitable for either gasoline or E85 may lead to an underestimated or overestimated average fuel economy value. For instance, a fuel density set for E85 will result in an overestimated average fuel economy when the engine is operating on lower density gasoline, and a fuel density set for gasoline will result in an underestimated average fuel economy when the engine is operating on higher density E85. Further, neither will be accurate when the alcohol/gasoline blend is somewhere between 100% gasoline and 100% E85.